The invention relates generally to film-cooled parts and more particularly to a method for quantifying hole flow rates in film cooled parts.
Gas turbines and other high-temperature equipment use film cooling extensively for effective protection of the hot gas path components, such as turbine blades. Film cooling refers to a technique for cooling a part in which cool air is discharged through a plurality of small holes in the external walls of the part to provide a thin, cool barrier along the external surface of the part and prevent or reduce direct contact with hot gasses.
Accurate knowledge of the film hole flow rates is required to determine how each part should behave compared to the design intent. Inspection of parts to measure these flow rates determines the acceptability of the parts for use, and hence, also has a large impact on cost and rework. Such inspection or measurement can be used to help determine the life or remaining life of a part. Inspection of serviced parts determines their ability to be returned to service.
The standard method for the measurement of film hole flow rates is known as “flow checks”. A flow check measures the total flow through a part placed on a test stand. Comparisons to either gauge measurements on good parts and/or analytic models of the flow circuits determines the acceptability. Typically, this process is so time consuming that only overall parts are flow checked, or at best some individual film rows, but never individual film holes. Furthermore, there is no way to distinguish between two parts which may have very different internal thermal performance (heat transfer coefficients), but which flow the same amount and otherwise pass all external dimensional tests.
One technique that overcomes or alleviates the foregoing disadvantages or drawbacks of the prior art is directed to a method for measuring a flow rate in a cooling hole of a film cooled part comprising measuring a transient thermal response of an external surface temperature of the film cooled part near film cooling holes; mathematically characterizing the transient thermal response; and determining the flow rate from the characterization. Although this technique overcomes or alleviates many of the disadvantages described above, it requires knowledge of hole spacing, orientation and shaping as well as precision in consistently locating the same surface points near holes in each part. It would therefore be advantageous to provide a method for quantifying hole flow rates in film cooled parts without the need for precisely and consistently locating the same surface measurement points near holes in each film cooled part or knowledge of hole spacing, orientation and shaping.